The present invention relates to molding apparatus and methods, and more particularly to apparatus and methods for molding onto a loaded, elastic blank.
The development of high tech fabrics has permitted the incorporation of fabric into a wide variety of applications not previously consider appropriate for fabrics. For example, certain high tech fabrics have been developed that include a weave of multifilament yarns and elastomeric monofilaments. These fabrics provide remarkable load bearing characteristics, while at the same time providing appropriate elasticity to be comfortable as a load bearing fabric in seating applications. More specifically, these fabrics are now widely used to form the seats and backs of office chairs and other seating structures. To enable attachment of the fabric to a chair seat or other support structure, it is known to mold a mounting component directly onto the fabric. The mounting component is typically molded about the periphery of the fabric to provide a structure that can be mounted to a frame or other support structure. In many applications, it is desirable to mount the fabric to the chair in a stretched (or loaded) condition primarily because the stretched fabric provides more desirable comfort characteristics. The desire to have a loaded fabric complicates the manufacturing process—at least with respect to the process of molding the mounting component onto the fabric.
One current process for manufacturing chair components with a loaded fabric is to stretch the fabric before it is placed in the mold for forming the mounting component. In one known embodiment of this process, the fabric is stretched prior to molding using a stretching machine that is located remotely from the mold. An operator loads a section of fabric into the stretching machine. The stretching machine clamps the fabric around its periphery and stretches the fabric to the desired tension. Once stretched, the fabric is shuttled to a loom station. At this station, a loom is closed onto the fabric to hold it in the stretched condition. The loom is then moved to the mold and positioned so that the fabric is properly oriented with respect to the mold surfaces. The mold is closed about the fabric while it continues to be held in the stretched position by the loom. Once the molding process is complete, the loom carrying the fabric and attached mounting component are removed from the mold and returned to the loom station. The loom is removed at the loom station and the fabric and attached mounting component are returned to the operator. The assembly is finished, for example, by trimming the excess fabric from the assembly. Although effective, this process and the associated apparatus suffer from various disadvantages. For example, the apparatus is relatively expensive because it requires a stretching machine, a loom and a mold that are specially configured to interact with one another. Also, this process results a relatively large amount of waste fabric, which can be a significant problem because of the high cost of high tech fabrics. With this process, the fabric must include a significant peripheral marginal portion that can be gripped and held during the stretching, looming and molding steps. This marginal portion must be large enough not only to extend outside of the mold to the loom but also outside of the loom to the stretching machine. After molding, this peripheral marginal portion serves no function and is trimmed away and discarded as waste. Further, once the fabric is stretched, it begins to decay at the locations where it is attached to the stretching machine or loom due to the focused stress. The decay continues until such time as the mounting component is formed to distribute the stretching forces over a greater portion of the fabric. This apparatus also requires a relatively large amount of floor space to accommodate the separate stretching machine, loom machine and mold. Additionally, the apparatus presents quality control concerns. The apparatus utilizes strain gauges in the stretching machine to apply the desired stretch to the fabric. In operation, the stretching machine monitors the amount of resistance provided by the stretched fabric. Once the predetermined resistance is reached, the stretching device stops stretching the fabric and the loom is closed onto the fabric. Once the loom is closed on the fabric, the system no longer knows anything about the state or condition of the fabric. This can present problems because the fabric is under a significant load and may partially separate from the loom in one location or another. Any separation or other defects that arise after the loom is installed will go unnoticed by the system. This may result in defective parts.
A number of methods have been developed that overcome some of the disadvantages of this apparatus. In one alternative, the fabric is stretched by the closing action of the mold. In this alternative, the edges of the fabric are held and the mold parts are specially shaped so that movement of the mold parts together causes the fabric to stretch. This process requires a specific amount of stretch to be built into the mold and does not provide the ability to adjust the stretch. In another alternative, hydraulic components are included in the mold. The hydraulic components are moved after the fabric has been closed in the mold to apply the desired amount of stretch. Although providing some benefits, these alternative methods continue to suffer from a variety of problems ranging from high cost to product quality issues.